Update wpr installation

This is being updated because the old one doesn't work on a modern mac
(which is where I do the page recording for page load tests), so we need
to have a more modern one. This required a bit of change to srnamed, but
actually made the code wildly simpler (woohoo!)
Make srrun handle mac AND development in virtualenv

This way we can use it locally to run the wpr exploder (coming in the
next commit), which needs access to our local copy of the wpr library.
Add wprexplode

This is a tool to take an archive created by web-page-replay and explode
it into a set of files and apache config for the stone ridge apache
servers to consume.